ИСТИНА

Tin-containing zeolites have been demonstrated to be promising catalysts for many industrially important reactions. It is generally accepted that the outstanding catalytic properties of Sn-BEA material are due to isolated Sn sites which isomorphically substitute silicon in zeolite lattice. But the localization of Sn-sites in real zeolite material is still a big question. In this contribution we report on the application of 1D and 2D 119Sn MAS NMR experiments modified by Carr-Purcell-Meiboom-Gill (CPMG) echo-train acquisition to elucidate the structure and localization of the different Sn-sites in fully dehydrated Sn-BEA zeolite synthesized in fluorine media (Sn/Si=0.005). The application of CPMG echo-train acquisition solves the problem of NMR sensitivity (signal to noise gain > 30)[1] and allow getting the high-resolution spectra even in such techniques like rotational echo double resonance (REDOR) и 2D magic-angle tuning (MAT)[2]. Basing on 119Sn{1H} CP/MAS NMR, DP-CPMG with and without 1H-decoupling and the analysis of CPMG echoes it was found that non-defective Sn-BEA material can be obtained by optimized pretreatment procedure. According to the 1H–119Sn REDOR-CPMG data the average distance from tin to nearest defects (OH-groups) was more than 8Å. The attribution of the narrow 119Sn signals to specific sites in T-positions of BEA framework was carried out on the basis of the analysis CSA parameters measured by 2D MAT-CPMG experiment and their comparison with theoretical calculations[3]. These groups are then assigned to the following three groups of T-sites: I - T9, T4 and T3; II – T2, T1 and T8; III – T7, T5 and T6. The results reveal that the sites of the third group are the most populated in studied Sn-BEA material.